Temperature overload relay



Patented Aug. 18, 1936 UNITED STATES PATENT OFFICE Charles H. Chapman,Scotia, N. Y., assignor to General Electric Company, a corporation ofNew York Application October 5, 1935, Serial No. 43,741

4 Claims.

My invention relates to relays, more particularly to thermal overloadrelays having an inverse time characteristic, and has for an object theprovision of a simple, reliable and inexpensive 5 relay of this type.

Various thermal overload relays have heretofore been proposed forprotecting electrical energy translating apparatus against overloads ofsuflicient magnitude and duration to subject the apparatus to dangeroustemperatures. In applying thermal overload protection to such apparatus,it is often desirable or 'necessary that the entire control includingthe thermal relay, be immersed in a body of oil, as for instance, whenthe apparatus to be protected is located in a hazardous place which issubject to explosive or corrosive atmospheres, and consequentlyconsiderable need has arisen for a thermal overload relay which willoperate satisfactorily when immersed 20 in a body of oil. Y

The operation of thermal overload relays is to a large extent dependentupon the thermal properties of the medium surrounding the thermalworking parts of the relay, and serious operating 25 diiculties areencountered, therefore, in the design of thermal relays for oil immersedoperation. For example, the required watt input to operate a thermalrelay in air is increased by approximately 400% when the relay isimmersed 30 in a large body of oil.

This large watt input is of course unsatisfactory, and may be offset bythermally isolating the Working parts of the relay from the large bodyof oil. Resort may be had, for this purpose, to the 35 practice ofenclosing the thermal working parts of the relay in an oil-filled sealedcontainer of thermal insulating material, so that the relay parts arethermally associated with only a small body of oil which is thermallyisolated from the 40 main body of immersing oil.

Operating difliculties are again encountered, however, due to thesusceptibility of the sealed container to leakage. Uniform operation ofthe relay requires that the thermal parts of the relay 4" be subjectedat all times to the same ambient medium, and it will be apparent that ifthe sealed container develops a leak before the relay is immersed, or ifthe relay is removed from its oil bath after the leak occurs, the oilwithin the container 5U will drain out and the operation of the relaywill be considerably affected by the air which enters the container.When the relay container is immersed in oil after the oil originallysealed therein has escaped, it will be found that the air which istrapped Within the container will substantially prevent the containerfrom reiilling with oil, that is, a diving-bell effect exists. Theconstruction of a tightly sealed container may also involve considerableexpense.

Much is yet to be desired, therefore, in a ther- 5 mal relay suitablefor oil immersed operation in which provision is made for ensuring thatthe working parts of the relay'are subjected at all times to the properimmersing medium, the relay being designed for 10W Watt input whensubjected 10 to that medium. Accordingly, it is a further object of myinvention to provide a simple and inexpensive thermal relay theoperation of which is reliable and uniform when immersed in oil.

In carrying out my invention in one form, I provide walls of insulatingmaterial arranged to form a perforate container within which the thermaloperating parts of the relay are disposed. The degree of perforation issuch that when the relay is immersed in a body of oil, the containerwill be substantially filled with oil, while the thermal operating partsof the relay and the relatively small body of oil Within the containerare thermally insulated from the main body of oil so as to minimize thetransfer of heat therebetween. The thermal operating parts of the relaycomprise a suitable thermally responsive device and a heater thermallyassociated therewith. More specifically, I provide a container formed ofinsulating material, at least two walls of the container being providedwith apertures of such size as to provide a degree of perforation whichpermits the container to fill with oil when it is immersed, and whichprevents the entrapment of air within the container. Disposed Within thecontainer, I provide a plurality of thermal devices each of which isprovided with a heater. A pair of operating members extend through aWall of the container and are arranged to control suitable externallymounted contacts in accordance 40 with the thermal condition of eitheror both of the thermal devices.

For a more complete understanding of my invention, reference should nowbe had to the drawing in which Fig. 1 is an elevational view of a 45relay embodying my invention; Fig. 2 is a sectional view taken alongline 2-2 of Fig. 1; Fig. 3 is a sectional View taken along line 3-3 ofFig. 1 with certain parts broken away; and Fig. 4 is a somewhatdiagrammatic view of my improved thermal relay immersed in a body of oilWithin a tank or casing adapted to contain suitable load circuitcontrolling contactors or other devices.

Referring now to the drawing, I have shown my invention in one form asapplied to a thermal relay comprising a container i@ which includes aboxlike hollow member li formed of insulating material and provided witha cover member i2. As shown in Fig. 2, the opposed end walls i3 of thecontainer are provided with relatively small apertures i4 so as toprovide a perforate container. The size of the apertures id is such asto provide a predetermined degree of perforation so that when thecontainer is immersed in a body of oil, the containerwillbesubstantially filled with oil, the non-air-tight constructionpreventing the entrapment of air within the container. Furthermore, theapertures i4 are of such small size that the small body of oil withinthe container is substantially thermally insulated from the main body ofoil. Although the size of the apertures I4 may be varied somewhat inaccordance with particular installations, have found that for operationin an immersing medium having the viscosity of ordinary transformer oil,a diameter of 11g" provides satisfactory operation.

Disposed within the container iii, I provide a plurality of thermaldevices l5 and i6. Although these thermal devices may be of any suitabletype, I have shown for purposes oi illustration a pair of solder filmoverload relays of the type described and claimed in United StatesPatent No. 2,001,513 issued May 14, 1935 to Ernest Zurcher.

For vthe purposes of the present application each of the thermal devicesi5 and i@ which. are identical in construction, may be described ascomprising a rotatable shaft or sleeve il which is normally soldered toa cylinder iii supported on a base i9 formed of insulating material. Thebase I9 is provided with terminal screws 20 and 2i which serve tosupport conductors 22 and 23 each oi which is provided with an extendingportion arranged to engage a suitable terminal post. As shown, theconductor 22 engages the terminal post 24 which extends through and issecured to a wall of the container IIE, and the conductor 23 engages asimilar terminal post 25.

As described in the above referred to patent to Zurcher, a heatingwinding 26 encircles the cylinder I8, the ends of the heating windingbeing secured to and supported by a pair of hollow rivets 21 and 28carried by a cover member 29. As shown, when the cover member 29 ispositioned on the base member I9 and secured by suitable nuts 30 whichengage the terminal posts 20 and 2|, the rivets 2l and 28 respectivelyengage the conductors 22 and 23, and the heater winding 26 is thereforeconnected in circuit with the terminal members 24 and 25. It Will beunderstood of course that when a predetermined current ilows through theheating winding 26 for a denite time, the fusible solder which normallysecures the shaft II to the cylinder I8 will be fused, and accordingly,the shaft Il will be released for rotation relative to the cylinder i8.

While the thermal devices l5 and i6 may be arranged to operate anysuitable contact mechanism, I have shown for purposes of illustration anarrangement by means of which a single pair of contacts 3| and 32 may beoperated in accordance with the thermal condition of either or both ofthe thermal devices I5 and i6. As shown, each of the shafts II carries atoothed wheel 33, the toothed wheel 33 associated with the thermaldevice I5 being arranged to engage a rack 34 which carries the movablecontact 3l and the toothed wheel 33 associated with the thermal deviceI6 being arranged to engage a rack 35 which carries the contact 32. Asshown, a suitable insulating member 3Ia is interposed between thecontact 3l and the rack 34 and a similar insulating member 32a isinterposed' between the. contact 32 and the rack 35 so as electricallyto insulate the contacts from the racks. It will be understood that thecontacts are connected in a circuit to be controlled by suitableconductors (not shown) for example, in thecircuit of the operating coilof a contacter which controls the load circuit in which the heaters 26are connected.

The rack 34 is provided adjacent its upper end with a slot 36, and ascrew 3l' extending from a. Wall of the container i@ cooperates with theslot ,3 6 to guide the rack 3ft for reciprocal longitudinal movement.Likewise the lower end of the rack 35 is provided with a slot 38 whichcooperates with a screw 39 to guide the rack 35. EX- tending outwardlyfrom the rack 34 is a nger 40 to which is connected one end of anoperating spring 4l, the other end of the spring being connected to asimilar iinger 42 which extends outwardly from the rack 35. As shown,the lower end of the rack 34 extends through and is guided by a slot inthe arm 42, a suitable spring 43 connected between'the arm 42 and thelower end of the rack 34 serving to bias the rack into engagement withits associated gear 33. Likewise the upper end of the rack 35 extendsthrough a slot in the finger 4U, and a spring i4 biases the rack 35 intoengagement with its associated gear 33. Suitable stop pins 45 and ditassociated respectively with the racks 34 and 35 are provided forlimiting the reciprocal longitudinal movement of the racks when releasedby the thermal devices for operation by the spring ffii.

It is now believed that a complete understanding of my invention may behad from a description of the operation. It will first be assumed thatthe container iii has been immersed in a body of oil along with suitableload circuit controlling contactors and other devices, and that thethermal devices i5 and i6 have been connected in the circuit to beprotected by means of the terminals 24 and 25. In Fig. 4, for example, Ihave shown the container iti immersed in a body of oil 50 contained in atank or casing 5I. Preferably, the container Ill is mounted on apanelboard 52 by means of the terminal studs 24 and 25, and it will beunderstood that the casing 5I also contains the load circuit controllingcontactors or other devices (not shown) immersed in the body of oil 50,the contacts 3| and 32 of the thermal relay being connected by flexibleleads (not shown) in a suitable control circuit, for example, theenergizing circuit of the contactors.

When the container I0 is immersed in the bath of oil, the apertures I4will permit oil to iiow into the container I0 and will also permit airto escape from the container I0 so that the container will besubstantially iilled with oil. So long as normal current flows in thecircuit to be protected, the relatively small body of oil Within thecontainer I 0 will absorb sucient heat from the heater 26 so as toprevent operation of the thermal devices. Under continued normal currentoperating conditions, a condition of heat equilibrium is established,the oil within the container being heated to a temperature such that therate of heat transmission from it to the outside body of oil is justequal to the rate of heat generation by the heaters 26. The amount ofthis heat, transmitted by conduction through the walls of the containerand by the slight amount of thermal circulation of oil through theapertures I4, is so Small, however, that the current operatingcharacteristics of the relay are substantially independent of the volumeof the relatively large body of oil in which the relay, along with theload circuit controlling device, is immersed. Upo`n the occurrence of anoverload in the circuit, however, the heat generated by the flow ofcurrent through the heater 26 will be suilicient to fuse the soldernormally securing the shaft I1 to the cylinder I8, and consequently, theshaft and the gear 33 carried thereby will be released for rotation inaccordance with the bias applied by the spring 4| and the associatedrack.

If it is assumed that the thermal device I is heated suiciently torelease the associated gear 33 for rotation, it will be apparent thatthe rack 34 will be moved downwardly by the spring 4| so as to disengagethe contact 3| from the contact 32. Likewise if the thermal device I6 isheated sufficiently to release its gear 33 for rotation, it will beapparent that the rack 35 will be moved upwardly by the spring 4I tomove the contact 32 away from the contact 3|.

The contact 3| may be reset after the thermal device I5 has cooled bypressing upwardly on the lower end of the rack 34, the spring 43permitting the rack to slide over the teeth of the gear 33. Similarly,the contact 32 may be reset after the thermal device I6 has cooled.

Although I have shown a particular contact arrangement and a particulartype of thermal device, it will be understood that my invention is notlimited thereto, since any suitable type of thermal device such, forexample, as a bimetallic element may be mounted within the perforatecasing IU.

As used throughout the specication and the claims, the term oil" will beunderstood to mean any suitable insulatingliquid medium.

While I have shown a particular embodiment of my invention, it will beunderstood, of course, that I do not wish to be limited thereto sincemany modications may be made and I, therefore, contemplate by theappended claims to cover any such modications as fall within the spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A thermal relay for operation in a relatively large body of oil withoil immersed load circuit controlling devices, said relay being immersedin the same body of oil as said load circuit controlling devicescomprising a' unitary structure including walls of thermal insulatingmaterial arranged to form a perforate container, the degree ofperforation being such as to permit said container substantially to fillwith oil when said unitary structure is immersed, the relatively smallbody of oil within the container being thermally insulated by said wallsfrom the main body of oil, a thermal device disposed within saidcontainer, and means within said container for heating said thermaldevice,

2. A thermal relay for operation in a relatively large body of oil withoil inmiersed load circuit controlling devices, said relay beingimmersed in the same body oi.' oil as said load circuit controllingdevices, comprising walls of thermal insulating material arranged toform a container, at least two of said walls having restricted aperturestherein, said apertures being proportioned to permit said containersubstantially to ll with oil when said container is immersed in a bodyof oil, the relatively small body of oil within said container beingthermally insulated by said walls from the main body of oil, a thermalelement disposed within said container, a heating winding disposed inthermal relation to said thermal element within said container, andmeans including circuit connections extending through a wall of saidcontainer for energizing said heating winding thermally to influencesaid thermal element.

3. A thermal relay adapted for oil immersed operation comprising wallsof thermal insulating material arranged to form a perforate container,the degree of perforation being such as to permit said containersubstantially to fill with oil when said container is immersed in a bodyof oil, the relatively small body of oil within the container beingthermally insulated by said walls from the main body of oil, a thermaldevice Within said container including a rotatable member extendingthrough a wall of said container, fusible means normally restrainingsaid member against rotation, heating means disposed within saidcontainer for heating said fusible means to release said member, andcircuit controlling contacts responsive to rotation of said member.

4. A thermal relay for operation in a, relatively large body of oil withoil immersed load circuit controlling devices, said relay being immersedin the same body of oil as said load circuit controlling devices,comprislng walls made of heat insulating material forming a container,said walls being provided with a relatively small aperture for admissionof oil to fill said container when it is immersed but substantiallypreventing thermal circulation of oil between the oil in said containerand the oil surrounding said container, a pair of switch contacts, heatresponsive means in said container for controlling the operation of atleast one of said contacts, current responsive heat generating means insaid container for heating said heat responsive means in response to thecurrent in said heat generating means for operation of said contactsupon the occurrence of a predetermined current, said walls providingthermal insulation substantially to prevent the transfer of heat byconduction therethrough from the oil in said container t0 the oilsurrounding said container, said walls thereby serving to admit oil toll said container when the container is immersed while thermallyisolating the oil in said container from the oil surrounding saidcontainer so that the current responsive operating characteristics ofsaid relay are substantially independent of the volume of the body ofoil in which it is immersed.

CHARLES H. CHAPM`AN.

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